RFID tags replying using changed reply timing

ABSTRACT

RFID tags and chips for RFID tags are capable of replying using changed reply timing. In a number of embodiments, this timing change is achieved when a tag receives a custom timing command from an RFID reader. In some embodiments, the changed reply timing affects an amount of delay before a tag backscatters a reply.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S.A. Provisional Application No.60/902,745, filed on 2007 Feb. 21, the disclosure of which is herebyincorporated by reference for all purposes.

This application claims priority from U.S.A. Provisional Application No.61/005,232 filed on 2007 Dec. 4, the disclosure of which is herebyincorporated by reference for all purposes.

This application may be found to be related to U.S. patent applicationSer. No. 1,203,397 by the same inventors, titled “CAUSING RFID TAGS TOREPLY USING CHANGED REPLY TIMING”, filed by the same assignee on thesame day as the instant application.

FIELD OF THE INVENTION

The present description is about Radio Frequency IDentification (RFID)systems, and more specifically for systems where RFID tags reply toreaders using changed reply timing.

BACKGROUND

Radio Frequency IDentification (RFID) systems typically include RFIDtags and RFID readers. RFID readers are also known as RFIDreader/writers or RFID interrogators. RFID systems can be used in manyways for locating and identifying objects to which the tags areattached. RFID systems are particularly useful in product-related andservice-related industries for tracking objects being processed,inventoried, or handled. In such cases, an RFID tag is usually attachedto an individual item, or to its package.

In principle, RFID techniques entail using an RFID reader to interrogateone or more RFID tags. The reader transmitting a Radio Frequency (RF)wave performs the interrogation. The RF wave is typicallyelectromagnetic, at least in the far field. The RF wave can also bepredominantly electric or magnetic in the near field.

A tag that senses the interrogating RF wave responds by transmittingback another RF wave. The tag generates the transmitted back RF waveeither originally, or by reflecting back a portion of the interrogatingRF wave in a process known as backscatter. Backscatter may take place ina number of ways. In addition, tags usually have prescribed replytimings for replying by backscattering.

The reflected-back RF wave may further encode data stored internally inthe tag, such as a number. The response is demodulated and decoded bythe reader, which thereby identifies, counts, or otherwise interactswith the associated item. The decoded data can denote a serial number, aprice, a date, a destination, other attribute(s), any combination ofattributes, and so on.

An RFID tag typically includes an antenna system, a radio section, apower management section, and frequently a logical section, a memory, orboth. In earlier RFID tags, the power management section included anenergy storage device, such as a battery. RFID tags with an energystorage device are known as active or semi-active tags. Advances insemiconductor technology have miniaturized the electronics so much thatan RFID tag can be powered solely by the RF signal it receives. SuchRFID tags do not include an energy storage device, and are calledpassive tags.

It is desired to have RFID systems with additional capabilities, forimproved functionality.

BRIEF SUMMARY

The invention improves over the prior art.

Briefly, the present invention provides RFID reader systems, readers,components, software and methods for causing RFID tags to reply usingchanged reply timing. In a number of embodiments, this timing change isachieved by causing a custom timing command to be transmitted to a tag.In some embodiments, the changed reply timing affects an amount of delaybefore a tag backscatters a reply.

The present invention also provides RFID tags and chips for RFID tagsthat are capable of replying using changed reply timing. In a number ofembodiments, this timing change is achieved when a tag receives a customtiming command from an RFID reader. In some embodiments, the changedreply timing affects an amount of delay before a tag backscatters areply.

The invention offers the advantage that some tags can be processeddifferentially from others, which can improve the functionality of awhole RFID system that processes RFID-tagged items. Additionally, thefact that the tags can actually perform the feature can serve as averification criterion that the tags are not counterfeit. Moreover, someembodiments can enhance the privacy of the owners of items tagged withsuch tags.

These and other features and advantages of the invention will be betterunderstood from the specification of the invention, which includes thefollowing Detailed Description and accompanying Drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The following Detailed Description proceeds with reference to theaccompanying Drawings, in which:

FIG. 1 is a block diagram of components of an RFID system.

FIG. 2 is a diagram showing components of a passive RFID tag, such as atag that can be used in the system of FIG. 1.

FIG. 3 is a conceptual diagram for explaining a half-duplex mode ofcommunication between the components of the RFID system of FIG. 1.

FIG. 4 is a block diagram showing a detail of an RFID reader system,such as the one shown in FIG. 1.

FIG. 5 is a block diagram of a whole RFID reader system according toembodiments.

FIG. 6 is a block diagram illustrating an overall architecture of anRFID reader system according to embodiments.

FIG. 7 is a flowchart illustrating methods for an RFID reader systemcomponent according to embodiments.

FIG. 8 is a diagram illustrating commands that may be transmitted as aresult of operations of the flowchart of FIG. 7 according toembodiments.

FIG. 9A is a table illustrating the fields of the Select command of theGen2 Spec version 1.1.0, versions of which may be used as any one ormore of the commands of FIG. 8 according to embodiments.

FIG. 9B is a table illustrating how a number of custom commands can beenabled in a reader and a tag.

FIG. 9C is a table showing sample values that can be used for the tableof FIG. 9B.

FIG. 10 is a block diagram of an implementation of an electrical circuitformed in an IC of the tag of FIG. 2.

FIG. 11 is an optional partial state diagram of a state machine of a taghaving an electrical circuit as shown in FIG. 10.

FIG. 12 is a flowchart illustrating methods for a tag according toembodiments.

FIG. 13 is two timing diagrams for illustrating how a reply timing canbe changed according to some embodiments.

FIG. 14 is a conceptual timing diagram for illustrating how an amount ofdelay in the reply timings of the embodiments of FIG. 13 can be furthertuned.

DETAILED DESCRIPTION

The present invention is now described. While it is disclosed in itspreferred form, the specific embodiments of the invention as disclosedherein and illustrated in the drawings are not to be considered in alimiting sense. Rather, these embodiments are provided so that thisdisclosure will be thorough and complete, and will fully convey thescope of the invention to those skilled in the art. Indeed, it should bereadily apparent in view of the present description that the inventionmay be modified in numerous ways. Among other things, the presentinvention may be embodied as devices, methods, software, and so on.Accordingly, the present invention may take the form of an entirelyhardware embodiment, an entirely software embodiment, an entirelyfirmware embodiment, or an embodiment combining aspects of the above.This description is, therefore, not to be taken in a limiting sense.

The invention is now described in more detail.

FIG. 1 is a diagram of components of a typical RFID system 100,incorporating aspects of the invention. An RFID reader 110 transmits aninterrogating Radio Frequency (RF) wave 112. RFID tag 120 in thevicinity of RFID reader 110 may sense interrogating RF wave 112, andgenerate wave 126 in response. RFID reader 110 senses and interpretswave 126.

Reader 110 and tag 120 exchange data via wave 112 and wave 126. In asession of such an exchange, each encodes, modulates, and transmits datato the other, and each receives, demodulates, and decodes data from theother. The data is modulated onto, and demodulated from, RF waveforms.

Encoding the data in waveforms can be performed in a number of differentways. For example, protocols are devised to communicate in terms ofsymbols, also called RFID symbols. A symbol for communicating can be adelimiter, a calibration symbol, and so on. Further symbols can beimplemented for ultimately exchanging binary data, such as “0” and “1”,if that is desired. In turn, when the waveforms are processed internallyby reader 110 and tag 120, they can be equivalently considered andtreated as numbers having corresponding values, and so on.

Tag 120 can be a passive tag or an active or semi-active tag, i.e.having its own power source. Where tag 120 is a passive tag, it ispowered from wave 112.

FIG. 2 is a diagram of an RFID tag 220, which can be the same as tag 120of FIG. 1. Tag 220 is implemented as a passive tag, meaning it does nothave its own power source. Much of what is described in this document,however, applies also to active tags.

Tag 220 is formed on a substantially planar inlay 222, which can be madein many ways known in the art. Tag 220 includes an electrical circuit,which is preferably implemented in an integrated circuit (IC) 224. IC224 is arranged on inlay 222.

Tag 220 also includes an antenna for exchanging wireless signals withits environment. The antenna is usually flat and attached to inlay 222.IC 224 is electrically coupled to the antenna via suitable antenna ports(not shown in FIG. 2).

The antenna may be made in a number of ways, as is well known in theart. In the example of FIG. 2, the antenna is made from two distinctantenna segments 227, which are shown here forming a dipole. Many otherembodiments are possible, using any number of antenna segments.

In some embodiments, an antenna can be made with even a single segment.Different points of the segment can be coupled to one or more of theantenna ports of IC 224. For example, the antenna can form a singleloop, with its ends coupled to the ports. It should be remembered that,when the single segment has more complex shapes, even a single segmentcould behave like multiple segments, at the frequencies of RFID wirelesscommunication.

In operation, a signal is received by the antenna, and communicated toIC 224. IC 224 both harvests power, and responds if appropriate, basedon the incoming signal and its internal state. In order to respond byreplying, IC 224 modulates the reflectance of the antenna, whichgenerates the backscatter from a wave transmitted by the reader.Coupling together and uncoupling the antenna ports of IC 224 canmodulate the reflectance, as can a variety of other means.

In the embodiment of FIG. 2, antenna segments 227 are separate from IC224. In other embodiments, antenna segments may alternately be formed onIC 224, and so on.

The components of the RFID system of FIG. 1 may communicate with eachother in any number of modes. One such mode is called full duplex.Another such mode is called half-duplex, and is described below.

FIG. 3 is a conceptual diagram 300 for explaining the half-duplex modeof communication between the components of the RFID system of FIG. 1,especially when tag 120 is implemented as passive tag 220 of FIG. 2. Theexplanation is made with reference to a TIME axis, and also to a humanmetaphor of “talking” and “listening”. The actual technicalimplementations for “talking” and “listening” are now described.

RFID reader 110 and RFID tag 120 talk and listen to each other by takingturns. As seen on axis TIME, when reader 110 talks to tag 120 thecommunication session is designated as “R→T”, and when tag 120 talks toreader 110 the communication session is designated as “T→R”. Along theTIME axis, a sample R→T communication session occurs during a timeinterval 312, and a following sample T→R communication session occursduring a time interval 326. Of course interval 312 is typically of adifferent duration than interval 326—here the durations are shownapproximately equal only for purposes of illustration.

According to blocks 332 and 336, RFID reader 110 talks during interval312, and listens during interval 326. According to blocks 342 and 346,RFID tag 120 listens while reader 110 talks (during interval 312), andtalks while reader 110 listens (during interval 326).

In terms of actual technical behavior, during interval 312, reader 110talks to tag 120 as follows. According to block 352, reader 110transmits wave 112, which was first described in FIG. 1. At the sametime, according to block 362, tag 120 receives wave 112 and processesit, to extract data and so on. Meanwhile, according to block 372, tag120 does not backscatter with its antenna, and according to block 382,reader 110 has no wave to receive from tag 120.

During interval 326, tag 120 talks to reader 110 as follows. Accordingto block 356, reader 110 transmits a Continuous Wave (CW), which can bethought of as a carrier signal that ideally encodes no information. Asdiscussed before, this carrier signal serves both to be harvested by tag120 for its own internal power needs, and also as a wave that tag 120can backscatter. Indeed, during interval 326, according to block 366,tag 120 does not receive a signal for processing. Instead, according toblock 376, tag 120 modulates the CW emitted according to block 356, soas to generate backscatter wave 126. Concurrently, according to block386, reader 110 receives backscatter wave 126 and processes it.

In the above, an RFID reader/interrogator may communicate with one ormore RFID tags in any number of ways. Some such ways are calledprotocols. A protocol is a specification that calls for specific mannersof signaling between the reader and the tags.

One such protocol is called the Specification for RFID AirInterface—EPC™ Radio-Frequency Identity Protocols Class-1 Generation-2UHF RFID Protocol for Communications at 860 MHz-960 MHz, which is alsocolloquially known as “the Gen2 Spec”. The Gen2 Spec has been ratifiedby EPCglobal, which is an organization that maintains a website at:<http://www.epcglobalinc.org/> at the time this document is initiallyfiled with the USPTO.

In addition, a protocol can be a variant of a stated specification suchas the Gen2 Spec, for example including fewer or additional commandsthan the stated specification calls for, and so on. In such instances,additional commands are sometimes called custom commands.

FIG. 4 is a block diagram showing a detail of an RFID reader system 410,which can be the same as reader 110 shown in FIG. 1. A unit 420 is alsoknown as a box 420, and has at least one antenna driver 430. In someembodiments it has four drivers 430. For each driver 430 there is anoutput device for a connector. The output device is typically a coaxialcable plug. Accordingly connectors 435 can be attached to the outputdevices of the provided respective drivers 430, and then connectors 435can be attached to respective antennas 440.

A driver 430 can send to its respective antenna 440 a driving signalthat is in the RF range, which is why connector 435 is typically but notnecessarily a coaxial cable. The driving signal causes the antenna 440to transmit an RF wave 412, which is analogous to RF wave 112 of FIG. 1.In addition, RF wave 426 can be backscattered from the RFID tags,analogous to RF wave 126 of FIG. 1. Backscattered RF wave 426 thenultimately becomes a signal sensed by unit 420.

Unit 420 also has other components 450, such as hardware and/or softwareand/or firmware, which may be described in more detail later in thisdocument. Components 450 control drivers 430, and as such cause RF wave412 to be transmitted, and the sensed backscattered RF wave 426 to beinterpreted. Optionally and preferably there is a communication link 425to other equipment, such as computers and the like, for remote operationof system 410.

FIG. 5 is a block diagram of a whole RFID reader system 500 according toembodiments. System 500 includes a local block 510, and optionallyremote components 570. Local block 510 and remote components 570 can beimplemented in any number of ways. It will be recognized that reader 110of FIG. 1 is the same as local block 510, if remote components 570 arenot provided. Alternately, reader 110 can be implemented instead bysystem 500, of which only the local block 510 is shown in FIG. 1. Plus,local block 510 can be unit 420 of FIG. 4.

Local block 510 is responsible for communicating with the tags. Localblock 510 includes a block 551 of an antenna and a driver of the antennafor communicating with the tags. Some readers, like that shown in localblock 510, contain a single antenna and driver. Some readers containmultiple antennas and drivers and a method to switch signals among them,including sometimes using different antennas for transmitting and forreceiving. And some readers contain multiple antennas and drivers thatcan operate simultaneously. A demodulator/decoder block 553 demodulatesand decodes backscattered waves received from the tags via antenna block551. Modulator/encoder block 554 encodes and modulates an RF wave thatis to be transmitted to the tags via antenna block 551.

Local block 510 additionally includes an optional local processor 556.Processor 556 may be implemented in any number of ways known in the art.Such ways include, by way of examples and not of limitation, digitaland/or analog processors such as microprocessors and digital-signalprocessors (DSPs); controllers such as microcontrollers; softwarerunning in a machine such as a general purpose computer; programmablecircuits such as Field Programmable Gate Arrays (FPGAs),Field-Programmable Analog Arrays (FPAAs), Programmable Logic Devices(PLDs), Application Specific Integrated Circuits (ASIC), any combinationof one or more of these; and so on. In some cases some or all of thedecoding function in block 553, the encoding function in block 554, orboth, may be performed instead by processor 556.

Local block 510 additionally includes an optional local memory 557.Memory 557 may be implemented in any number of ways known in the art.Such ways include, by way of examples and not of limitation, nonvolatilememories (NVM), read-only memories (ROM), random access memories (RAM),any combination of one or more of these, and so on. Memory 557, ifprovided, can include programs for processor 556 to run, if provided.

In some embodiments, memory 557 stores data read from tags, or data tobe written to tags, such as Electronic Product Codes (EPCs), TagIdentifiers (TIDs) and other data. Memory 557 can also include referencedata that is to be compared to the EPC codes, instructions and/or rulesfor how to encode commands for the tags, modes for controlling antenna551, and so on. In some of these embodiments, local memory 557 isprovided as a database.

Some components of local block 510 typically treat the data as analog,such as the antenna/driver block 551. Other components such as memory557 typically treat the data as digital. At some point there is aconversion between analog and digital. Based on where this conversionoccurs, a whole reader may be characterized as “analog” or “digital”,but most readers contain a mix of analog and digital functionality.

If remote components 570 are indeed provided, they are coupled to localblock 510 via an electronic communications network 580. Network 580 canbe a Local Area Network (LAN), a Metropolitan Area Network (MAN), a WideArea Network (WAN), a network of networks such as the internet, or amere local communication link, such as a USB, PCI, and so on. In turn,local block 510 then includes a local network connection 559 forcommunicating with network 580.

There can be one or more remote component(s) 570. If more than one, theycan be located at the same location, or in different locations. They canaccess each other and local block 510 via network 580, or via othersimilar networks, and so on. Accordingly, remote component(s) 570 canuse respective remote network connections. Only one such remote networkconnection 579 is shown, which is similar to local network connection559, etc.

Remote component(s) 570 can also include a remote processor 576.Processor 576 can be made in any way known in the art, such as wasdescribed with reference to local processor 556.

Remote component(s) 570 can also include a remote memory 577. Memory 577can be made in any way known in the art, such as was described withreference to local memory 557. Memory 577 may include a local database,and a different database of a Standards Organization, such as one thatcan reference EPCs.

Of the above-described elements, it is advantageous to consider acombination of these components, designated as operational processingblock 590. Block 590 includes those that are provided of the following:local processor 556, remote processor 576, local network connection 559,remote network connection 579, and by extension an applicable portion ofnetwork 580 that links connection 559 with connection 579. The portioncan be dynamically changeable, etc. In addition, block 590 can receiveand decode RF waves received via antenna 551, and cause antenna 551 totransmit RF waves according to what it has processed.

Block 590 includes either local processor 556, or remote processor 576,or both. If both are provided, remote processor 576 can be made suchthat it operates in a way complementary with that of local processor556. In fact, the two can cooperate. It will be appreciated that block590, as defined this way, is in communication with both local memory 557and remote memory 577, if both are present.

Accordingly, block 590 is location agnostic, in that its functions canbe implemented either by local processor 556, or by remote processor576, or by a combination of both. Some of these functions are preferablyimplemented by local processor 556, and some by remote processor 576.Block 590 accesses local memory 557, or remote memory 577, or both forstoring and/or retrieving data.

Reader system 500 operates by block 590 generating communications forRFID tags. These communications are ultimately transmitted by antennablock 551, with modulator/encoder block 554 encoding and modulating theinformation on an RF wave. Then data is received from the tags viaantenna block 551, demodulated and decoded by demodulator/decoder block553, and processed by processing block 590.

The invention also includes methods. Some are methods of operation of anRFID reader or RFID reader system. Others are methods for controlling anRFID reader or RFID reader system.

These methods can be implemented in any number of ways, including thestructures described in this document. One such way is by machineoperations, of devices of the type described in this document.

Another optional way is for one or more of the individual operations ofthe methods to be performed in conjunction with one or more humanoperators performing some of them. These human operators need not becollocated with each other, but each can be only with a machine thatperforms a portion of the program.

The invention additionally includes programs, and methods of operationof the programs. A program is generally defined as a group of steps oroperations leading to a desired result, due to the nature of theelements in the steps and their sequence. A program is usuallyadvantageously implemented as a sequence of steps or operations for aprocessor, such as the structures described above.

Performing the steps, instructions, or operations of a program requiresmanipulation of physical quantities. Usually, though not necessarily,these quantities may be transferred, combined, compared, and otherwisemanipulated or processed according to the steps or instructions, andthey may also be stored in a computer-readable medium. These quantitiesinclude, for example, electrical, magnetic, and electromagnetic chargesor particles, states of matter, and in the more general case can includethe states of any physical devices or elements. It is convenient attimes, principally for reasons of common usage, to refer to informationrepresented by the states of these quantities as bits, data bits,samples, values, symbols, characters, terms, numbers, or the like. Itshould be borne in mind, however, that all of these and similar termsare associated with the appropriate physical quantities, and that theseterms are merely convenient labels applied to these physical quantities,individually or in groups.

The invention furthermore includes storage media. Such media,individually or in combination with others, have stored thereoninstructions of a program made according to the invention. A storagemedium according to the invention is a computer-readable medium, such asa memory, and is read by a processor of the type mentioned above. If amemory, it can be implemented in a number of ways, such as Read OnlyMemory (ROM), Random Access Memory (RAM), etc., some of which arevolatile and some non-volatile.

Even though it is said that the program may be stored in acomputer-readable medium, it should be clear to a person skilled in theart that it need not be a single memory, or even a single machine.Various portions, modules or features of it may reside in separatememories, or even separate machines. The separate machines may beconnected directly, or through a network such as a local access network(LAN) or a global network such as the Internet.

Often, for the sake of convenience only, it is desirable to implementand describe a program as software. The software can be unitary, orthought in terms of various interconnected distinct software modules.

This detailed description is presented largely in terms of flowcharts,algorithms, and symbolic representations of operations on data bits onand/or within at least one medium that allows computational operations,such as a computer with memory. Indeed, such descriptions andrepresentations are the type of convenient labels used by those skilledin programming and/or the data processing arts to effectively convey thesubstance of their work to others skilled in the art. A person skilledin the art of programming may use these descriptions to readily generatespecific instructions for implementing a program according to thepresent invention.

Embodiments of an RFID reader system can be implemented as hardware,software, firmware, or any combination. It is advantageous to considersuch a system as subdivided into components or modules. A person skilledin the art will recognize that some of these components or modules canbe implemented as hardware, some as software, some as firmware, and someas a combination. An example of such a subdivision is now described.

FIG. 6 is a block diagram illustrating an overall architecture of anRFID reader system 600 according to embodiments. It will be appreciatedthat system 600 is considered subdivided into modules or components.Each of these modules may be implemented by itself, or in combinationwith others. It will be recognized that some aspects are parallel withthose of FIG. 7. In addition, some of them may be present more thanonce.

RFID reader system 600 includes one or more antennas 610, and an RFFront End 620, for interfacing with antenna(s) 610. These can be made asdescribed above. In addition, Front End 620 typically includes analogcomponents.

System 600 also includes a Signal Processing module 630. In thisembodiment, module 630 exchanges waveforms with Front End 620, such as Iand Q waveform pairs. In some embodiments, signal processing module 630is implemented by itself in an FPGA.

System 600 also includes a Physical Driver module 640, which is alsoknown as Data Link. In this embodiment, module 640 exchanges bits withmodule 630. Data Link 640 can be the stage associated with framing ofdata. In one embodiment, module 640 is implemented by a Digital SignalProcessor.

System 600 additionally includes a Media Access Control module 650,which is also known as MAC layer. In this embodiment, module 650exchanges packets of bits with module 640. MAC layer 650 can be thestage for making decisions for sharing the medium of wirelesscommunication, which in this case is the air interface. Sharing can bebetween reader system 600 and tags, or between system 600 with anotherreader, or between tags, or a combination. In one embodiment, module 650is implemented by a Digital Signal Processor.

System 600 moreover includes an Application Programming Interface module660, which is also known as API, Modem API, and MAPI. In someembodiments, module 660 is itself an interface for a user.

All of these functionalities can be supported by one or more processors.One of these processors can be considered a host processor. Such aprocessor would, for example, exchange signals with MAC layer 650 viamodule 660. In some embodiments, the processor can include applicationsfor system 600. In some embodiments, the processor is not considered asa separate module, but one that includes some of the above-mentionedmodules of system 600.

A user interface 680 may be coupled to API 660. User interface 680 canbe manual, automatic, or both. It can be supported by a separateprocessor than the above mentioned processor, or implemented on it.

It will be observed that the modules of system 600 form something of achain. Adjacent modules in the chain can be coupled by the appropriateinstrumentalities for exchanging signals. These instrumentalitiesinclude conductors, buses, interfaces, and so on. Theseinstrumentalities can be local, e.g. to connect modules that arephysically close to each other, or over a network, for remotecommunication.

The chain is used in opposite directions for receiving and transmitting.In a receiving mode, wireless waves are received by antenna(s) 610 assignals, which are in turn processed successively by the various modulesin the chain. Processing can terminate in any one of the modules. In atransmitting mode, initiation can be in any one of these modules.Ultimately, signals are transmitted internally, for antenna(s) 610 totransmit as wireless waves.

The architecture of system 600 is presented for purposes of explanation,and not of limitation. Its particular subdivision into modules need notbe followed for creating embodiments according to the invention.Furthermore, the features of the invention can be performed eitherwithin a single one of the modules, or by a combination of them.

An economy is achieved in the present document in that a single set offlowcharts is used to describe methods in and of themselves, along withoperations of hardware and/or software and/or firmware. This isregardless of how each element is implemented.

Methods are now described more particularly according to embodiments.Such methods may be practiced by different embodiments, including butnot limited to RFID reader system components as described above. Inaddition, individual operations of such methods may be practiced bydifferent readers, at different phases of the lifetime of an RFID tag,with or without interruptions between them, and so on.

In some embodiments, a first command is caused to be transmitted to theRFID tag. The first command is of course encoded in an electromagneticwave such as wave 112, according to a communication protocol. Suchprotocols specify a number of such commands, and any such command can beconsidered to be the first command. Such commands can include, forexample, command requesting a handle, such as a random number, or a moreidentifying number such as a TID or an EPC. A number of additionalpossible first commands are also described below in more detail, butthat is only for example and not for limitation.

In some embodiments, a backscattered first reply is received from thetag, responsive to the first command having been transmitted. A reply tothe first command can be considered as the first reply for purposes ofthis document. The first reply uses a first reply timing as the replytiming, and such tag reply timings are described in more detail later inthis document.

The first command can be sent to a tag that has been singulated from atag population. In other instances, the tag has not yet been singulated.

In one class of examples, the first command can be any of the commandsissued in an exchange for commissioning a tag, where data is written inits memory, and an acknowledging reply is backscattered. It is known,therefore, that a tag that has been commissioned has received such afirst command, and has replied to it.

FIG. 7 is flowchart 700 for illustrating some methods according toembodiments. In some embodiments, at optional operation 710 of FIG. 7,the first command is a command for the tag to identify itself to thereader. In some instances, operation 710 can be used for identifying thetag, and therefore knowing that it is capable of replying using achanged reply timing, as described in the present document. If operation710 is not performed, however, the first command can be considered anyother command in the exchange.

In some embodiments, at optional operation 720, an identifying reply isreceived as the first reply. These embodiments are preferably where thefirst command is operation 710. Again, if operation 720 is notperformed, the first reply can be considered any other reply that areader has done with a tag.

Operation 770 of flowchart 700 is now described. While the descriptionof operation 770 is somewhat out of turn for the flow of flowchart 700,it is presented at this point in the document so that the description ofthe additional optional operations of flowchart 700 taking place beforeoperation 770 will make sense.

At operation 770, a custom timing command is caused to be transmitted tothe tag, after receiving the first reply. In response to receiving thecustom timing command, when the tag later backscatters a second reply,that second reply uses a second reply timing that is different from thefirst reply timing. Again, examples of such second replies and suchsecond reply timings are described in more detail later in thisdocument.

It will be appreciated that operation 770 may be performed either by thesame reader as the one that transmitted the first command, or by adifferent reader. In either case, the tag may or may not have lost powerafter backscattering the first reply, and before receiving the customtiming command. In embodiments where a reader processes a tag that hasalready been commissioned, operation 770 takes place. In addition, afirst command may or may not have been transmitted. If it has been, thenit may or may not be operation 710.

The custom timing command can be generated in any number of ways. Forexample, it can be automatic, or triggered by any number of events. Oran instruction can be received by one of the modules of FIG. 7, and beobeyed. In some embodiments, where operation 720 has taken place, theinstruction can be generated and received responsive to parsing theidentifying reply. In such instances, for example, it can be discernedfrom the identifying reply that the tag supports the custom timingcommand, and the instruction is thus generated. Then bits can bereceived, or looked up from a table stored in a memory, and so on. Thesebits can be prepared into one or more packets for transmission, and soforth.

In some embodiments, the tag is able to backscatter the second replyusing the second reply timing regardless of what state it is in, at thetime it receives the custom timing command of operation 770.

In other embodiments, the tag can have two states, namely an enabledstate and a disabled state, as will be described in more detail later inthis document. Briefly, if the tag is in the enabled state, it canoperate as per the above. But if the tag is in the disabled state, if itwere to receive the custom timing command, the second reply timing wouldnot be different from the first reply timing, even if it backscatteredthe second reply.

In embodiments of the latter case, at an optional next operation 760, anEnable command can be caused to be transmitted while the tag is in thedisabled state. In some instances, this would cause the tag totransition internally to the enabled state. In some instances, theEnable command can be the first command described above. In these cases,therefore, the second reply timing is different from the first replytiming responsive to receiving the custom timing command while the tagis in the enabled state.

An optional operation 780 can take place after operation 770. Accordingto operation 780 a Disable command can be caused to be transmitted tothe tag, while the tag is in the enabled state. This can cause the tagto transition internally to the disabled state.

FIG. 8 is a diagram illustrating commands that may be transmitted as aresult of operations of the flowchart of FIG. 7 according toembodiments. A wave 812 is a special case of wave 112 of FIG. 1. AnEnable command 860 is optionally sent first, according to operation 760.A custom timing command 870 is sent next, according to operation 770.Then a Disable command 880 is optionally sent, according to operation780.

As will be realized, commands 860, 870, 880 can be configured in anynumber of ways. For example, if Enable command 860 is provided, it canbe separate from custom timing command 870. Preferably, these areconfigured as separate standalone commands, each occurring at a singleone of the communication sessions such as those of time interval 312 ofFIG. 3. In addition, the tag need not backscatter a reply to any one ofthem individually.

In addition, command 870, plus optionally commands 860 and 880, may beused among other commands that will be transmitted to the tag inquestion, and possibly other tags. Equally, the optional first andsecond replies will be among other replies backscattered by the tag inquestion, and possibly other tags.

In some embodiments, a reader system component can perform a methodaccording to flowchart 700 to communicate with a single tag. This can beaccomplished if the tag is the only one in its field of view. Or, thetag in question can be within a population of tags, but it has beensingulated. This means that the tag in question is the only one from thepopulation that replies to the reader.

In other embodiments, a reader component can perform a method accordingto flowchart 700 to communicate with more than one tag. For example,custom timing command 870 can be transmitted to a population of tags,intending that they each backscatter a second reply using the secondreply timing, either together, or at different times, or in response tosubsequent commands.

In yet other embodiments, combinations are possible. For example, Enablecommand 860 might be sent to a population of tags before one of them issingulated. Then, custom timing command 870 might be sent to a tag thathas been singulated, or to whole the population of tags.

Each one of commands 860, 870, 880 can be constructed in any number ofways. In some instances, they can be considered as custom commands asnot being specified in a particular communication protocol. In someinstances they would be standalone commands, made by a sequence of bitschosen so that they do not conflict with other commands of the protocol.In other instances, they can be commands with a custom payload. Suchcommands can be known to the protocol or not, and the payload can beused to distinguish among different custom commands, and optionallyfurther transfer a parameter for the commands.

When commands are used that are known to the protocol, a section oftheir payload can be advantageously used for the purpose of implementinga custom command, such as commands 860, 870, 880. For example, it can bean enable payload, a disable payload, etc. Such a section in the payloadcan be a mask field, according to embodiments. For the Gen2 Spec, twosuch commands are the Select command and the BlockWrite command. Betweenthese two candidate commands, it should be considered that the Selectcommand can be transmitted before or after a tag is singulated out ofits population, while the BlockWrite is better suited for singulatedtags. In addition, the BlockWrite command is optional to the Gen2 Spec,and the tag would probably have to have a controller that can accept it.

Each one of commands 860, 870, 880 can thus be constructed as animplementation of this Select command or the BlockWrite command. Inaddition to responding to the payload implementing the custom command,the tag may further, or may not also respond to the underlying Selectcommand or BlockWrite command. An example is now described in terms ofthe Select command, but would apply equally to the BlockWrite command.

FIG. 9A is a table illustrating the fields of the Select command of theGen2 Spec. Version 1.1.0 of the Gen2 Spec is hereby incorporated byreference in its entirety. The fields of this Select command areexplained in more detail in the above mentioned Gen2 Spec. In addition,the implementation of this Select command can have a custom payload sothat it operates as Enable command 860, custom timing command 870,Disable command 880, and/or another custom command.

FIG. 9B is a table illustrating how a number of custom commands can beenabled in a reader and a tag. EBV stands for Extensible Bit Vector. TheMask Field can be partitioned as shown, into two primary subfields,named FEF and FCF.

The Feature Enabling Field (FEF) enables the tag to verify that it is aproper recipient for the command, by comparing the transmitted FEF valueagainst a value in Membank. In this case, Membank can be EPC, TID orUSER memory. As can be seen, the FEF can be further partitioned intosubfields, for better clarity. Such subfields can include a ClassIdentifier, the MDID, and an Indicator Bit.

The Class Identifier can be two bits. For example, EPCglobal cancorrespond to a value of 10. This would allow the custom command toapply, for example, only to EPCglobal tags.

The MDID is the tag manufacturer's ID, which is stored in the tag's TIDmemory. For Impinj tags, this number is 000000000001 or 100000000001.The MDID allows a reader to select tags of only the manufacturer ofinterest. So, even if this Select command is transmitted and receivedbefore singulation, the Select command can select also according to thetag manufacturer's ID. This will cause the manufacturer's tags to beselected, and thus the reader can ensure prior knowledge of the tagmanufacturer's identification.

The Indicator Bit can be set to 0 or 1. In the Gen2 spec, a tag modelnumber follows the MDID. A bit of this model number can serve as theIndicator Bit, and can be interpreted as follows: If it is 0, the tagscan interpret the command as an “ordinary” Select, and execute it perthe Gen2 spec. Else, if it is 1, the tags can interpret the Selectcommand as a custom instruction, and execute according to the FCF.

The Feature Command Field (FCF) can have a command code that indicatesthe number of the custom instruction. For example, a command code of00000 could be the custom timing command. This permits 31 possiblecustom commands. In addition, a command code of 11111 could indicate anextended command code that extends into the subsequent data field.

The data field can contain data needed to implement the custominstruction, if any. Not all commands will use it. The data field can bevariable in size. Its meaning will derive from the command codes.

In some embodiments, the tag may ignore the Target and Action field inthe Select command, depending on whether these fields are relevant tothe CI. In other embodiments, the tag may also set the appropriate flag.

In preferred embodiments, the entire Select command must be valid forthe tag to accept and execute the custom command. That means validvalues for Membank, Length, Pointer, Mask, CRC-16, etc. An example isnow described.

FIG. 9C is a table showing sample values that can be used for the tableof FIG. 9B. These could be used for a custom timing command. The Membankhaving a binary value of 10 point to the TID memory. The pointer havinga hex value of 06 h points to the last two bits of the class identifier.The length having a hex value of 14 h points to a length of 20 bits thatfollow thereafter.

Everything described above in terms of readers and reader componentsfinds some correspondence with tags and tag chips. In some instances,some of the above also describe features and behavior of tag chips.

FIG. 10 is a block diagram of an electrical circuit 1024 according toembodiments. Circuit 1024 may be formed in an IC of an RFID tag, such asIC 224 of FIG. 2. Circuit 1024 has a number of main components that aredescribed in this document. Circuit 1024 may have a number of additionalcomponents from what is shown and described, or different components,depending on the exact implementation.

Circuit 1024 includes at least two antenna connections 1032, 1033, whichare suitable for coupling to one or more antenna segments (not shown inFIG. 10). Antenna connections 1032, 1033 may be made in any suitableway, such as using pads and so on. In a number of embodiments more thantwo antenna connections are used, especially in embodiments where moreantenna segments are used.

Circuit 1024 includes a section 1035. Section 1035 may be implemented asshown, for example as a group of nodes for proper routing of signals. Insome embodiments, section 1035 may be implemented otherwise, for exampleto include a receive/transmit switch that can route a signal, and so on.

Circuit 1024 also includes a Power Management Unit (PMU) 1041. PMU 1041may be implemented in any way known in the art, for harvesting raw RFpower received via antenna connections 1032, 1033. In some embodiments,PMU 1041 includes at least one rectifier, and so on.

In operation, an RF wave received via antenna connections 1032, 1033 isreceived by PMU 1041, which in turn generates power for components ofcircuit 1024. This is true for either or both R→T and T→R sessions,whether or not the received RF wave is modulated.

Circuit 1024 additionally includes a demodulator 1042. Demodulator 1042demodulates an RF signal received via antenna connections 1032, 1033.Demodulator 1042 may be implemented in any way known in the art, forexample including an attenuator stage, an amplifier stage, and so on.

Circuit 1024 further includes a processing block 1044. Processing block1044 receives the demodulated signal from demodulator 1042, and mayperform operations. In addition, it may generate an output signal fortransmission.

Processing block 1044 may be implemented in any way known in the art.For example, processing block 1044 may include a number of components,such as a processor, memory, a decoder, an encoder, and so on.

In a number of embodiments, processing block 1044 includes a statemachine 1048. State machine 1048 retains the state of the tag, at leastwhile circuit 1024 is powered. The state of the tag dictates which ofthe subsequently received commands the tag would respond to and how, andso on. State machine 1048 can be as is called for in the specifiedcommunications protocol, and adapted to further accommodate the customtiming command, with or without contradicting the operation of theprotocol.

Circuit 1024 additionally includes a modulator 1046. Modulator 1046modulates an output signal generated by processing block 1044. Themodulated signal is transmitted by driving antenna connections 1032,1033, and therefore driving the load presented by the coupled antennasegment or segments. Modulator 1046 may be implemented in any way knownin the art, for example including a driver stage, amplifier stage, andso on.

In one embodiment, demodulator 1042 and modulator 1046 may be combinedin a single transceiver circuit. In another embodiment, modulator 1046may include a backscatter transmitter or an active transmitter. In yetother embodiments, demodulator 1042 and modulator 1046 are part ofprocessing block 1044.

Circuit 1024 additionally includes a memory 1050, which stores data1052. Memory 1050 is preferably implemented as a Nonvolatile Memory(NVM), which means that data 1052 is retained even when circuit 1024does not have power, as is frequently the case for a passive RFID tag.

As already mentioned above, in some embodiments the custom timingcommand works only when the tag is in an enabled state, as opposed to adisabled state. An example is now described.

FIG. 11 is an optional partial state diagram 1148 of a state machine ofa tag having an electrical circuit as shown in FIG. 10. State diagram1148 can be implemented by state machine 1048. State diagram 1148includes enabled state 1165, and disabled state 1185, which can bestates as described above. In addition, an Enable command 1160 and aDisable command 1180 can be as described above. For example, the Enablecommand can cause the tag to transition to enabled state 1165. This canbe either only from disabled state 1185, or by remaining there fromenabled state 1165, and so on.

In some embodiments, enabled state 1165 and disabled state 1185 areprovided in a way that does not define additional states in theunderlying protocol. For example, for the Gen2 Spec, the initial Readystate can be a disabled state 1185, while one or more of the otherstates can be enabled states 1165. Or some of the other states can alsobe disabled state 1185.

In other embodiments, either one or both of enabled state 1165 anddisabled state 1185 can be provided as states different from, and inaddition to what is required by the Gen2 Spec. It should be remembered,however, that the invention may also be practiced with embodiments wherethe tag is always enabled to respond appropriately to the custom timingcommand by changing its reply timing, and has no disabled state.

Methods for RFID tags and tag chips are now described. These methods maybe practiced by different embodiments, including but not limited to thetag embodiments described above. Such methods may be performed by anumber of tags concurrently, or by a single tag, alone in a field ofview or singulated from a population, as has already been describedabove. In addition, it will be recognized that such methods will beperformed largely in response to reader methods, such as those offlowchart 700.

In some embodiments, a first command is received from an RFID reader.This would be the first command described above, as having beentransmitted towards the tag.

Then a first reply is backscattered optionally by the tag responsive toreceiving the first command. The first reply can be any reply specifiedby an applicable protocol for the first command. The first reply uses afirst reply timing, which is typically a reply timing specified by theprotocol, but can be any other reply timing.

FIG. 12 is flowchart 1200 illustrating sample methods for RFID tagsaccording to embodiments. It will be recognized that a method accordingto flowchart 1200 will be performed largely in response to the method offlowchart 700 being performed.

According to optional operation 1210, a command to identify is received,which is the command caused to be transmitted at optional operation 710.In some embodiments, the command to identify can be considered to be theabove-mentioned first command.

At optional operation 1220, an identifying reply is backscattered inresponse to the command, which is the reply received at operation 720.The identifying reply can be, for example, a random number, anElectronic Product Code (EPC), a TID, or other code stored in memorythat identifies the tag or item it is attached to, or its capabilitiesto change its reply timing. In some embodiments, the identifying replycan be considered to be the above-mentioned first reply.

Operation 1270 of flowchart 1200 is now described. While the descriptionof operation 1270 is somewhat out of turn for the flow of flowchart1200, it is presented at this point in the document so that thedescription of the additional optional operations of flowchart 1200taking place before operation 1270 will make sense.

At operation 1270, a custom timing command is received by the tag. Thecustom timing command is as described elsewhere in this document.Operation 1270 may be performed either at the same time as receiving thefirst command, or at a different time, e.g. by a different reader. Forexample, the first command may be received at a time that the tag iscommissioned, while the custom timing command may be received months oryears later. In such cases, the tag may have lost power afterbackscattering the first reply, and before receiving the custom timingcommand. In other instances, operation 1270 takes place during the sameexchange as receiving the first command, without even losing power.

At a later operation 1275, the tag backscatters a second reply, whichuses a second reply timing. The second reply timing is different fromthe first reply timing of the first reply, because the custom timingcommand has been received. This can be accomplished by the tag makingappropriate internal adjustments, in operating its modulator. Inaddition, some of these adjustments may involve setting an internalflag, adjusting an internal state machine, and so on.

In some embodiments, the second reply is backscattered in response toreceiving the custom timing command. In other embodiments, one or moreintervening commands are received after the custom timing command, andthe second reply is backscattered in response to receiving the one ofthese intervening commands.

In some embodiments, the reply timing is changed by the custom timingcommand only for the second reply, and the tag then reverts to using thefirst reply timing. In other embodiments, the reply timing is changedfor more than one of the subsequent replies. For example, the tag couldthen receive a third command, and backscatter a third reply, with thethird reply using a third reply timing different from the first replytiming. The third reply timing could be the same as or different thanthe second reply timing.

The effect of the custom timing command may or may not survive aninterim loss of power, after the custom timing command is received. Insome embodiments, the reply timing is changed permanently, while inothers, if power is lost, the tag will reset to replying using the firstreply timing.

As also mentioned above, in some embodiments, the tag is able tobackscatter the second reply using the second reply timing regardless ofwhat state it is in, at the time it receives the custom timing commandaccording to operation 1270. In other optional embodiments, the tag canhave two states, namely an enabled state and a disabled state, asdescribed with reference to FIG. 11.

At optional operation 1260, the tag can receive an Enable command, suchas the one transmitted at operation 760. At next operation 1265, the tagtransitions internally to enabled state 1165. This can be done inpreparation of operation 1270, when the custom command is received.

At optional operation 1280, the tag can receive a Disable command, suchas the one transmitted at operation 780. At next operation 1285, the tagtransitions internally back to disabled state 1185. This can be doneafter operation 1270, to cause the tag to revert to using the firstreply timing in its further replies. The Disable command is notnecessary to be implemented. For example, the tag could be automaticallydisabled after the second reply, or after a few replies, or uponreverting to another one of the specified states such as the Ready stateof the Gen2 spec.

In addition, in the event that any of the received commands, such as thecustom timing command, the Enable command, and the Disable command areimplemented by the Select command of FIG. 9A, the tag can respondproperly to it in addition to what is described with reference to thereply timings. For example, the tag can set or unset an internalselected flag, and so on. Plus, the tag may or may not issue a reply,since the Select command does not call for a reply. But it might, in acustom embodiment.

The reply timing can be changed in many different ways, as will beevident to a person skilled in the art in view of the presentdescription. In many such embodiments, the reply timing is a delay,before the tag starts backscattering, after receiving its most recentcommand, namely the command it is responding to. This works at least inthe Gen2 Spec, which calls for the vast majority of tag replies to bereceived within a specified time window after finishing transmitting acommand. Accordingly, readers may have a time window during which toreceive tag replies. Changing the delay may thus cause the tag reply tofall outside the window of readers that do not know better, as would beunauthorized readers. As such, practicing embodiments of the inventioncould increase privacy. Examples are now given.

FIG. 13 shows two timing diagrams 1310, 1330, for describing how thereply timing can change according to embodiments. Diagram 1310 shows afirst command 1320, which finishes being transmitted at time T0. Diagram1310 also shows a first reply 1325, backscattered in response to firstcommand 1310, and which starts being transmitted at time T1. Firstcommand 1320 and first reply 1325 can be the first command and the firstreply described above. Here the first delay is a between times T0 andT1. The first reply can include a functional content as called for theexchange by the protocol, for example a code stored in a memory, arandom number, and so on. Such a functional content is implemented byreplies whose bits are specified by the applicable protocol. Forexample, these replies for the Gen2 Spec are PC, EPC, RN16, etc.

Diagram 1330 shows an other command 1370, which finishes beingtransmitted at the same time T0, for comparison only with that ofdiagram 1310. Diagram 1330 also shows a second reply 1375, backscatteredin response to other command 1370, and which starts being transmitted attime T2. The most recent command for second reply 1375 has thus beenother command 1370, and thus second reply 1375 is has the second delaybetween times T0 and T2.

The reply timing has changed from diagram 1310 to diagram 1330, becausethe delay up to T2 is different than the delay up to T1, by an amountDT. It should be noted that, in this example, the delay up to T2 islonger than that up to T1, although that need not be the case. In fact,it could be the other way around. The changed reply timings can be usedto enhance the privacy of using the tag, by making it harder to read byunauthorized readers.

Other command 1370 could be either the custom timing command, or acommand that intervenes, being sent after the custom timing command. Infact, the custom timing command itself could call for no reply at all.

In addition, second reply 1375 encodes the same functional content asfirst reply 1325. In other words, second reply 1375 does the samefunction as first reply 1325, except that it is subject to a differentdelay. This can be accomplished in a number of ways. For example, secondreply 1375 can be identical to first reply 1325, having the same bits.Or the bits can be substantially similar from what they would be, withonly a few added or changed, for further preventing second reply 1375from being read by unauthorized readers. Or the bits can be totallydifferent, but still accomplish the same function.

FIG. 14 is a conceptual timing diagram for illustrating how an amount ofdelay DT in the reply timings of the embodiments of FIG. 13 can befurther tuned according to embodiments.

A Tune command 1470 is caused to be transmitted by the reader, andreceived by the tag. Tune command 1470 can be any convenient command,such as the first command, the custom timing command, or other commandin the communication. Tune command 1470 encodes a time-indicatingparameter. The time indicating parameter can be encoded as data in theFCF subfield shown in FIG. 9B. The second reply timing is thusdetermined from the time-indicating parameter. In an embodiment of areader component, the time-indicating parameter can be looked up from adesired value for the second reply timing.

In the example of FIG. 14, the time-indicating parameter is a two-bitfield code 1472. Here it is shown with the possible values it can take.Each value results in a different delay DT, namely one of DT1, DT2, DT3,and DT4. These values for delay DT can optionally be used in embodimentsof the invention such as those of FIG. 13. The delay DT can be expressedin number of clock cycles, in a number of RF cycles, or in other unitsof time convenient for this purpose. Thus, in one example, delay DT canhave values chosen among 4 msec, 8 msec, 12 msec, and 16 msec. Inaddition, such a delay should not be too long, because then othercommunication may start taking place.

Numerous details have been set forth in this description, which is to betaken as a whole, to provide a more thorough understanding of theinvention. In other instances, well-known features have not beendescribed in detail, so as to not obscure unnecessarily the invention.

The invention includes combinations and subcombinations of the variouselements, features, functions and/or properties disclosed herein. Thefollowing claims define certain combinations and subcombinations, whichare regarded as novel and non-obvious. Additional claims for othercombinations and subcombinations of features, functions, elements and/orproperties may be presented in this or a related document.

1. An Integrated Circuit (IC) chip for use with a Radio FrequencyIdentification (RFID) tag having an antenna, comprising: a processingblock that has received through the antenna a first command from an RFIDreader, and caused to be backscattered a first reply responsive toreceiving the first command, the first reply using a first delay beforethe tag starts backscattering the first reply after receiving the firstcommand, the processing block further operable to: receive a customtiming command from the RFID reader, and then backscatter a second replythat encodes the same functional content as the first reply, the secondreply using a second delay before the tag starts backscattering thesecond reply after receiving a most recent command prior tobackscattering the second reply, the second delay different from thefirst delay responsive to receiving the custom timing command.
 2. The ICchip of claim 1, in which the second reply is identical to the firstreply.
 3. The IC chip of claim 1, in which the second reply includesbits more than half of which are arranged similarly to those of thefirst reply.
 4. The IC chip of claim 1, in which the functional contentis one of a code stored in a memory, and a random number.
 5. The IC chipof claim 1, in which the tag loses power after backscattering the firstreply and before receiving the custom timing command.
 6. The IC chip ofclaim 1, in which the most recent command is the custom timing command.7. The IC chip of claim 1, in which the most recent command is anintervening command received after the custom timing command.
 8. The ICchip of claim 1, in which a third command is received after the secondreply is backscattered, and a third reply is backscattered, the thirdreply using a third delay different from the first delay responsive tohaving received the custom timing command.
 9. The IC chip of claim 8, inwhich the third delay is substantially the same as the second delay. 10.The IC chip of claim 1, in which the tag is able to backscatter thesecond reply using the second delay regardless of what state it is in atthe time it receives the custom timing command.
 11. The IC chip of claim1, in which the tag is in a disabled state where, if it were to receivethe custom timing command, the second delay would be the same as thefirst delay if it were to backscatter the second reply, the firstcommand is an Enable command received while the tag is in the disabledstate, and the chip transitions internally to an enabled stateresponsive to receiving the Enable command, the custom command therebybeing received while the tag is in the enabled state, the second delaybeing different from the first delay responsive to the tag receiving thecustom timing command while it is in the enabled state.
 12. The IC chipof claim 11, in which the Enable command is the Select command accordingto Gen2 Specification, and further having a special enable payload, andthe chip further transitions to the enabled state responsive to theSelect command having the special enable payload.
 13. The IC chip ofclaim 11, in which a Disable command is further received while in theenabled state and the chip transitions internally back to the disabledstate responsive to receiving the Disable command.
 14. The IC chip ofclaim 13, in which the Disable command is the Select command accordingto Gen2 Specification, and further having a special disable payload, andthe chip further transitions to the disabled state responsive to theSelect command having the special disable payload.
 15. The IC chip ofclaim 1, in which a Tune command is received, which encodes atime-indicating parameter, and the second delay is determined from thetime-indicating parameter.
 16. The IC chip of claim 15, in which theTune command is one of the first command and the custom timing command.17. A Radio Frequency Identification (RFID) tag, comprising: an antenna;and a circuit coupled to the antenna, the circuit including a processingblock that has received a first command from an RFID reader, and causedto be backscattered a first reply responsive to receiving the firstcommand, the first reply using a first delay before the tag startsbackscattering the first reply after receiving the first command, theprocessing block further operable to: receive a custom timing commandfrom the RFID reader, and then backscatter a second reply that encodesthe same functional content as the first reply, the second reply using asecond delay before the tag starts backscattering the second reply afterreceiving a most recent command prior to backscattering the secondreply, the second delay different from the first delay responsive toreceiving the custom timing command.
 18. A method for a Radio FrequencyIdentification (RFID) tag that has received a first command from an RFIDreader, and backscattering a first reply responsive to receiving thefirst command, the first reply using a first delay before the tag startsbackscattering the first reply after receiving the first command,comprising: receiving a custom timing command from the RFID reader; andthen backscattering a second reply that encodes the same functionalcontent as the first reply, the second reply using a second delay beforethe tag starts backscattering the second reply after receiving a mostrecent command prior to backscattering the second reply, the seconddelay different from the first delay responsive to receiving the customtiming command.
 19. The method of claim 18, in which the functionalcontent is one of a code stored in a memory, and a random number. 20.The method of claim 18, in which the tag loses power afterbackscattering the first reply and before receiving the custom timingcommand.
 21. The method of claim 18, in which the most recent command isthe custom timing command.
 22. The method of claim 18, furthercomprising: the most recent command is an intervening command receivedafter the custom timing command.
 23. The method of claim 18, in which aTune command is received, which encodes a time-indicating parameter, andthe second delay is determined from the time-indicating parameter.